1. Field of the Invention
The present invention relates to a state information managing method which is able to manage easily state information of respective communication units and also reduce a communication traffic volume required for management of state information in a communication system wherein a plurality of communication units for exchanging data communication mutually are connected to a bus, and a system embodying the same.
2. Description of the Prior Art
In a communication system in which a plurality of communication units are connected to a bus, respective communication units can exchange data communication mutually. At this time, since internal states of respective communication units are changed with the lapse of time, state information indicating the internal states have been managed by the communication units respectively.
As the state information management method, there has been such a method that, when the data management portion issues a state request to respective communication units, such respective communication units transmits a state response to the data management portion in response to the state request from the data management portion. However, according to this method, since the state request and the state response must be issued from respective communication units, an extensive communication traffic volume has been needed.
Therefore, there has been known the first method to reduce the communication traffic volume of the state request. In the first method, once the state request has been issued after a state information collecting destination has been identified clearly, the communication units which receive such state request have transmitted automatically state reports to the state information collecting destination subsequently every time when their states are changed. According to the first method, the communication traffic volume of the state request can be reduced.
However, according to the above first method, since information as for the state information collecting destination must be transmitted to respective communication units, communication for informing respective communication units of such information as for the state information collecting destination have not been able to be omitted.
In addition, as the second method to reduce the communication traffic volume of the state request, there has been a method set forth in Patent Application Publication (KOKAI) Hei 6-68000, for example. According to this method set forth in Patent Application Publication (KOKAI) Hei 6-68000, temporary addresses which are different from individual addresses are temporarily set, then such temporary addresses are distributed to any objective terminal devices on a transmission line, and then only the objective terminal devices can be controlled every temporary address by virtue of communication frames.
However, in the second method, the temporary addresses has had to be transmitted to respective terminal devices which need the state information. Therefore, according to the second method, it has been difficult to reduce the communication traffic volume smaller than that in the first method.